1. Field of the Invention
This invention relates generally to monolithically integrated bipolar circuits and, more particularly, to a gallium arsenide (GaAs) integrated circuit having transistors with only two of three terminals exposed at the semiconductor surface.
2. Background Art
The fabrication of a monolithically integrated circuit typically comprises a semi-insulating or high resistivity substrate with an active layer on a surface of the substrate. Conventional techniques for forming the active layer include epitaxial growth, diffusions, ion implantations, etching processes, etc. However, recent advancements in the technology have made it more feasible for certain applications to use conducting material for the substrate for providing power supply voltages to the circuit. Historically, silicon has been the most widely used material for the fabrication of semiconductors, but binary III-V compounds such as GaAs have been recently considered important because of a higher electron mobility providing faster switching, higher transconductance, and less charge storage.
ECL integrated circuits historically have been fabricated in silicon wherein each transistor has its base, collector and emitter electrodes accessible at the surface of the integrated circuit resulting in parasitic wiring capacitance proportional to the number of electrodes and a packing density limited by the number of electrodes. Furthermore, the performance capability of inverted bipolar transistors in silicon is limited since the collector is lightly doped, therefor substantially reducing the efficiency of this junction when operating as an emitter.
Thus, a bipolar ECL structure is needed that decreases the density of the integrated circuit by requiring only two eletrodes for each transistor be accessible at the semiconductor surface, decreases the parasitic wiring capacitance, and allows for transistor operation in the inverse mode.